Investigators at the University of Iowa propose to purchase an orthovoltage X-ray machine in order to replace an obsolete General Electric Maxitron 250 (250 kVp, 30 mA) X-ray machine. The Maxitron 250 is approaching 40 years old and service and parts are no longer routinely available nor are the service and parts guaranteed by the manufacturer. The proposed replacement X-ray machine is a Philips Industrial X- ray system model MG450, which is a constant potential, 450 kilovolt, 15 mA machine. The complete X-ray system is to be installed in an existing X-ray suite in the Radiation Research Laboratory at the University of Iowa. Dose rate projections for the MG450 X-ray machine show that manby of the projects now performed on the obsolete X-ray machine or on an alternate gamma-ray source could be irradiated in as little as half the present beam time. Furthermore, the significant "repair time" on the obsolete machine will be obviated by the new, replacement X-ray machine. The proposed X-ray machine will be used in NIH-supported research of six major users and at least six minor users, all of whom have pending NIH applications (or will submit June 1). Organizational and scientific expertise for the administration and safe operation of the X-ray facility are already in place at the University. The Radiation Research Laboratory has provided radiation services to investigators within and from outside the University for approxiamtely thirty years. The radiation facilities advisory committee, comprised of faculty from the RRL, are in nearly daily contact with each other, which ensures that attention to quality and efficiency in the radiation service is maintained. The proposed replacement X-ray machine will enable this important research service for NIH and other researchers to continue (nearly) without interruption.